Oil well drilling mud



Patented June 4, 1935 PATENT OFFICE 01L WEIL DRILLING MUD Thane K. Stinson, East St. Louis, 111., assignor to Geo. S. Mepham Corporation, East St. Louis, Ill., a corporation of Delaware No Drawing. Application February 19, 1935,

Serial No. 7,176

-' I dclaimsa (01; 255- 1) This invention relates to. the production of drilling mud primarily for use in the drilling of oil and gas wells for the purpose of carrying the cuttings out of the hole and of lining the walls 5 of the drill hole to prevent either flow of water 4 or gas from the outside formation into the dri hole and to prevent loss of drilling fluid from the hole into the formation through which the hole is being drilled.

Drilling muds are used in almost all rotary drilling operations for deep wellsfor oil and gas and serve several functions. .They are used primarily to lubricate the drill bit and to carry the cuttings from the hole and for this purpose, in

5 many instances, drilling muds made from native materials in the formation in which the well is drilled are sufficient. g

In cases where high gas pressure is encountered, it is often necessary, however, to add a 'material which will increase the specific. gravity of the drillingmud in order to increase its weight and hold down the gas pressures. For this purpose weighting materials, such as iron oxide and barytes, have been commonly used in accordance with the Stroud patents, No. 1,575,944 and No. 1,575,945. In other cases where porous, sandy or sloughy formations are encountered in the wall of the hole, it is necessary to use a material which will have a high colloidal dispersion so as to vproduce a viscous mud whichyby filtration of the liquid of the mud through the walls of the bore hole, will provide an impervious or substantially impervious lining along the walls of the drill holes which will prevent the loss of drilling mud to the surrounding formations and will prevent seepage of water, gas or slough of the surrounding formations into the hole. For this purpose bentonite has been found to 'behighly desirable because ofo the high viscosity which can be secured wlth'a' relatively small percentage of bentonite in the drilling mud. The bentonite, furthermore, has

the characteristic of forming a relatively thin butsubstantially impervious coating along the 45 walls of the bore hole which effectively walls of! the surrounding formation and prevents loss of drilling mud to the surrounding formation and also prevents seepage or sloughing from the formation into the drill hole. I 1 1 l Bentonite, howevenis a colloidal material of relatively low mechanical strength andwhile it serves admirably the function of controlling the viscosity of the muds and of preventing the setby bentonite alone is not sumcicntly dense in all instances to meet with practical conditions encountered and occasionally leads to difficulties.

In view of the fact that bentonite is a relatively expensive material for this purpose, it is desirable V 5 to increase the mechanical strength of the lining of the hole formed by a bentonite mud and to increase the density of the lining to thereby reduce the amountof bentonite necessary to provide an impervious wall, and it is the object of my invention to improve the bentonite wall structure of an oilor gas well by incorporating in the bentonite mud, and therefore in the lining of the wall formed therefrom, a material which will increase the mechanical strength and density of the lining of the bore hole without increasing the cost of the mud so as to thereby reduce the amount of bentonite used to accomplish the desired result.

Another object of the invention is to provide an improvement in drilling muds of the bentonite or high'gelatinous type which will facilitate the formation and handling of the drilling muds.

Another object of the invention is to provide an additive material for drilling muds which will have distinct color characteristics to facilitate spotting of the various formations through which the drill is passing and checking the returns of the drilling mud.

Various other objects and advantages will appear as the description of the invention proceeds.

I have discovered that the addition of a relatively small percentage of iron oxide, tripoli, or other material having a rough cellular flake or sponge-like structure to a bentonite drilling mud will produce a material increase in the strength 5 with the addition of 2% of iron oxide to a bentonite drilling mud, 10% less of the bentonite is used up in forming a wall of the same degree of i'mperviousnws than is used 'in the forming of aytvall along the bore of the hole from bentonite alone. This provides a thinner wall for the same degree of imperviousness and leads to less blocking of the hole by the wall formation and greater facility and-less disturbing of the wall tling and segregation of cuttings in the hole, the ,55 protective coating on the hereof the hole formed formation in the removal of the drill bit or in the applications of casings to the wall, etc as this thinner lining is more resistant to mechanical and frictional abrasion.

For example, with a mud containing 5% of bentonite in water and a drilling mud containing 5% of a mixture of 98% of bentonite and 2% of cellular iron oxide and a drilling mud containing 5% of a mixture of 90% of bentonite and 10% of limonite, the relative weight of filter cake along the bore of the hole to hold' back the same amount of water or water pressure is as follows Bentonite+2% Bentonite-l-l% 'Bentomte in water iron oxide limonite By simple calculation from the above table, it will be seen that with 2% of iron oxide the average weight of filter cake to hold back the same amount of waterpressure is over 10% less than the weight of an all bentonite wall to accomplish the same result, and with 10% of iron oxide added to the bentonite, the weight of the filter cake is an average of about1.0% to 20% less. than the weight of an all bentonite cake to accomplish the same results.

While the principles of my invention may be applied in various ways, I prefer to mix from 2% to 10% of iron oxide, tripoli or other porous cellular materials with dry bentonite by a suitable grinding operation orotherwise, so as to insure a fairly uniform distribution of the iron oxide or other cellular material through the dry bentonite, so that there will be no chance segregation of .the iron oxide or other cellular particles in the mud as might occur if the iron oxide were added to a premixed bentonite mud. This material is then shippedto the oil field where it is 'mixed with water inzsufiicient portions .to form a drilling mud of the desired viscosity;

In general a suspension of the iron oxidebentonite mixture in water will form a drilling" becausesiron oxide, tripoli, etc., are porous cellular materials which have an affinity for and are extremely easy to wet with water, whereas bentonite wets with extreme difiiculty, so that an iron oxide-bentonite mixture containing from 2% to of iron oxide is wetted'with greater ease.

than bentonite alone.

By using an iron oxide of distinctive color, such as a yellow oxide, it is possible to impart a distinctive color to the mud, which is very helpful in spotting the particular formation being penetrated by the drill at a given time and in showing the rate of circulation of the mud, etc.

While the increase in mechanical strength and density of the wall formed on the bore of the hole by the addition of a relatively small amount of iron oxide or other porous cellular materials may be explained in various ways, I believe that this unexpected increase in strength is due to the fact that the iron oxide or tripoli particles of the types used by me have a rough cellular sponge-like or plate-like structure. These particles are very much larger than the ultimate bentonite particle tonite particles so interlock with' the larger sponge-like particles of iron oxide that a stronger and more compact, uniform wall structure is formed than is possible with bentonite particles alone. When a layer of these reinforced bentonite particles is built up as a protecting wall along the bore of an oil well, the result is a denser coating of materially greater mechanical strength and much'rore impervious to water than a wall built of bentonite particles alone. Y

- While I do not wish to be bound in any manner by this theory of operation, it appears to be a correct explanation of. what happens when a small percentage of iron oxide is mixed with bentonite and at the same time explains why the inclusion of silica, sand and other particles of a rounded granular nature from the native mud or from the drill cutting in a bentonite drilling fluid leadsto the formation of a less dense and more porous wall than bentonite alone.

The iron oxide or other cellular or plate-like materials should be in a state of fine sub-division, preferably of the order of iron oxide as used in paint pigments, and should be in a granular or crystalline condition, preferably in the ferric state as distinguished from ferrous oxide which is sometimes found in cpmbination with bentongether by the surrounding matrix of bentonite particles, whereas coarser particlesfsuch as ,the cuttings from the drill or coarser sand particles from the native muds, do not act in the same manner.

The term bentonite" is used herein in a generic sense as including all clays having high, gelation characteristics whether they are true bentonites or not and is intended to include such gelatinous nautral materials as Mojave mud and other clays having geling properties similar to bentonite.

While I have attempted to explain the theory 'on iwln'ch the addition of a'small amount of iron oxide to a bentonite drilling mud results in a substantial increase in density and mechanical strength of the mud lining formed alongthe wall of the bore hole, it will be understood that I do not -wish to be limited to this theory of operation and in combination with 2% to 10% of iron oxide hav ing a cellular, sponge-like structure.

3. A drilling mud for use in the drilling of oil and gas wells consisting of an approximately 5% suspension of bentonite and iron oxide in water, the portion of iron, oxide relative to bentonite being from 2% to 10%.

4. The method of increasing the strength of a bentonite lining along the bore of an oil or gas well which comprises adding to the dry bentonite from 2% to 10% of a cellular, flak-y material, such as iron oxide, prior to forming the drilling mud, mixing with a liquid to form the drilling mud and introducing the drilling mud into the well whereby the cellular, flaky material will become distributed through the bentonite lining along the bore of the well to strengthen the same. V

5. In the art of boring or controlling oil or gas wells the process which comprises introducing into the well a wall-building fluid containing bentonite to which has been added from 2% to'10% of iron oxide.

6. In the art of boring or controlling oil or gas wells the process which comprises introducing into the well a wall-building fluid containing a colloidal gelatinous material and a small percentage of a flaky reinforcing material, such as iron oxide.

THANE K. STINSON. 

